1. Field
This document relates to a backlight unit irradiating light to a liquid crystal display (LCD) device, and more particularly, to an apparatus and method for driving a light source of a backlight unit.
2. Related Art
Applications of liquid crystal displays (LCDs) tend to extend gradually due to the characteristics that they are lighter and thinner and are driven with low power consumption. LCDs are used in portable computers such as notebook computers, office automation equipment, audio/video equipment, indoor/outdoor advertisement displays, and the like. Transmissive LCDs, making up the majority of LCDs, display an image by adjusting light incident from a backlight unit according to a data voltage by controlling a field applied to a liquid crystal layer.
As a light source of a backlight unit, a fluorescent lamp such as a cold cathode fluorescent lamp (CCFL) has been used, but recently, a light emitting diode (LED) having great advantages in terms of power consumption, weight, luminance, and the like, relative to an exiting fluorescent lamp, is employed. Brightness of a plurality of LEDs is controlled by a light source driver. In order to control brightness of LEDs, a light source driver uses pulse width modulation (PWM) in order to control brightness of LEDs. In the PWM, a duty ratio of an output dimming signal is equal to that of an input PWM signal, but a frequency of the output dimming signal may be independently controlled to be different from that of the input PWM signal. A general output dimming frequency is 10 kHz or higher, namely, very high.
An LCD uses an idle mode for reducing power consumption, in addition to a normal mode for normally displaying an image. In the idle mode, the LCD activates minimum power required for an operation, and in particular, a duty ratio of an output dimming signal is significantly lowered to below a predetermined value (e.g., 0.02%).
However, in the related art light source driving device using PWM, an operation logic of minimum 13 bits or greater is required to calculate an output dimming value of 0.02% or smaller implemented in an idle mode and designing a light source driver is complicated. In addition, in order to implement an output dimming value as low as about 0.02% in an output dimming frequency band as fast as about 20 kHz, a reference clock of 100 MHz or higher is required, and in this case, since the related art light source driver should be designed to process operation data according to the reference clock, a configuration thereof is inevitably complicated. As the light source driver is designed to be complicated, a size of the light source driver is increased and unit cost of a product is increased accordingly.